Acid rain linked to damaged lakes.

Acid rain linked to damaged lakes

Locked in sediments beneath many freshwater lakes is a fossil record of water acidity stretching back hundreds of years. These records are among the many pieces of evidence that have now led a National Academy of Sciences (NAS) panel to conclude that acid rain has damaged lakes in the northeastern United States.

Although some scientists had long suspected that such a connected exists, others had proposed alternative explations for fishless acid lakes -- from natural acidification to the effects of farming and lumbering (SN: 3/17/84, p. 164). The NAS study released last week, "Acid Deposition: Long-Term Trends," suggests that in certain cases, none of the alternative explanations accounts for lake acidity as fully as the effect of sulfur dioxide emissions from the burning of fossil fuels and the resulting acid deposition.

"The connection between acid rain and environmental damage is real," says James H. Gibson of Colorado State University in Ft. Collins, who chaired the panel, "but it is more variable and complex than many people have supposed." Individual lakes vary widely in their response to acid rain, he says. Nevertheless, the report goes a long way toward linking sulfur dioxide emissions with lake acidification. According to the Academy, this report is "the most comprehensive effort to date" to document acid rain causes and effects.

One important element in the study was the analysis of sediment cores taken from lake bottoms. The number and types of fossil microorganisms called diatoms found in different layers of these sediments provide a sensitive measure of lake acidity. "Diatom analysis is the best technique that we have available for inferring past [acidity] histories of lakes," says biologist Donald F. Charles of Indiana University in Bloomington.

The researchers discovered that natural acidification normally occurs over hundreds or thousands of years. In contrast, some lakes in New York's Adirondack Mountains suffered significant acidity increases over a period of 20 to 40 years in the middle of this century.

The study also notes that while the Northeast seems on the average to have suffered the most damage, the region has also seen a decline in sulfur dioxide emissions over the past decade. The effect of this is seen in somewhat lower levels of acidity and sulfur in rain and in some streams.

In the Southeast, however, "precipitation shows escalating levels of acidity and sulfur, reflecting the increase in industrial emissions," Gibson says. "There is also some evidence that streams in the region are now showing increased acidification."

Panel scientists did not look into the question of whether local or distant air pollution sources were more responsible for these effects. Another open question is the effect of acid deposition on forests.

The Academy report will probably intensify the debate over what should be done about acid rain. President Reagan is likely to endorse a report that earlier this year called for a $5 billion research program to develop new techniques for cleaning coal (SN: 1/18/86, p. 37).

However, many environmental groups now believe that this would be a step backward. The National Clean Air Coalition, based in Washington, D.C., says the United States should mandate an immediate 50 percent emissions reduction to complement a program Canada has already adopted. A group of senators has just introduced a bill calling for a nationwide, $6 billion plan to curb acid rain.

Not everyone is convinced that such measures are necessary. The National Coal Association in Washington, D.C., argues that with the increasing use of low-sulfur coal and with improved emission controls, sulfur dioxide emissions will decline over the next five years without further government action.